Xenoestrogens at Picomolar to Nanomolar Concentrations Trigger Membrane Estrogen Receptor-α–Mediated Ca(2+) Fluxes and Prolactin Release in GH3/B6 Pituitary Tumor Cells

Xenoestrogens (XEs) are widespread in our environment and are known to have deleterious effects in animal (and perhaps human) populations. Acting as inappropriate estrogens, XEs are thought to interfere with endogenous estrogens such as estradiol (E(2)) to disrupt normal estrogenic signaling. We investigated the effects of E(2) versus several XEs representing organochlorine pesticides (dieldrin, endosulfan, o′p′-dichlorodiphenylethylene), plastics manufacturing by-products/detergents (nonylphenol, bisphenol A), a phytoestrogen (coumestrol), and a synthetic estrogen (diethylstilbestrol) on the pituitary tumor cell subline GH3/B6/F10, previously selected for expression of high levels of membrane estrogen receptor-α. Picomolar to nanomolar concentrations of both E(2) and XEs caused intracellular Ca(2+) changes within 30 sec of administration. Each XE produced a unique temporal pattern of Ca(2+) elevation. Removing Ca(2+) from the extracellular solution abolished both spontaneous and XE-induced intracellular Ca(2+) changes, as did 10 μM nifedipine. This suggests that XEs mediate their actions via voltage-dependent L-type Ca(2+) channels in the plasma membrane. None of the Ca(2+) fluxes came from intracellular Ca(2+) stores. E(2) and each XE also caused unique time- and concentration-dependent patterns of prolactin (PRL) secretion that were largely complete within 3 min of administration. PRL secretion was also blocked by nifedipine, demonstrating a correlation between Ca(2+) influx and PRL secretion. These data indicate that at very low concentrations, XEs mediate membrane-initiated intracellular Ca(2+) increases resulting in PRL secretion via a mechanism similar to that for E(2), but with distinct patterns and potencies that could explain their abilities to disrupt endocrine functions.